This invention relates to the field of soldering electronic chips, such as laser diodes to heat sinks.
Considerable problems have occurred upon attempts to form a good solder bond between an electronic chip such as an AlGaAs laser diode chip and a heat sink made of copper. Copper is highly mobile and thus copper ions will drift through various contiguous layers to penetrate an electronic chip such as an LED, and due to its highly reactive nature, "poisons" the LED to adversely affect proper operation thereof.
For space applications, Cu heat sinks are not acceptable; BeO heat sinks being required. Such heat sinks contain unbonded oxygen which must be blocked from the In solder layer positioned above the BeO. The resulting indium oxide weakens the soldered bond, and furthermore has poor thermal conductivity which reduces the efficiency of the heat sink. Also the BeO contains other contaminates that must be prevented from drifting into the LED.